Ninja Turtles (IDW)

The Ninja Turtles are the protagonists of the IDW comic series, and sometimes of the spin-off series Teenage Mutant Ninja Turtles Universe and accompanying miniseries. Their origin is slightly different in this comic compared to other forms of Ninja Turtle media, as they are the reincarnations of four teenage ninja warriors from centuries ago, reborn as turtles and then mutated.

Trivia

From the time the Turtles mutated, up to at least The Trial of Krang, they have been identified socially as teenagers, with it strongly implied that all four of them were indeed real teenagers when their past human selves died centuries ago. In terms of the overall chronological age of their spiritual selves, they are at least as old as the birth years of their long-dead human selves. As turtles, their age has never been unambiguously determined, and the IDW continuity has remained just as ambiguous about the relative passage of time in-universe, making it unclear how much time has passed since their birth as turtles or since their mutation day except that they have remained teenagers during their entire mutant lives so far. This chronological ambiguity stands in direct contrast to the Mirage continuity, which eventually gave its Turtles a fixed birth year of 1970, and Mirage stories have variously depicted them at a different age depending on the chronological setting of the story during the characters' lifespans in the 20th and 21st centuries.